Lift truck mast tilting arrangement



March 12, 1968 c. D. GIBSON ETAL 3,372,823

LIFT TRUCK MAST TILTING ARRANGEMENT 4 Sheets-Shet 1 Filed Oct. 4, 1965' INVENTOR. fizz/6,64

March 12, 1968 c. D. GIBSON ETAL 3,372,823

LIFT TRUCK MAST TILTING ARRANGEMENT Filed Oct. 1965 4 Sheets-Sheet 2 FIG.

(OJ INVEN'I'OR.

(D u I M h 1 1968 c. D. GIBSON ETA'L 3,3 2,3 3

LIFT TRUCK MAST TILTING ARRANGEMENT Filed Oct. 4, 1965 4 Sheets-Sheet 3 m i m U) o E 52 i Ll.

INVENTOR.

March 12,1968 D. GIBSON ETAL 3,372,823

LIFT TRUCK MAST TILTING ARRANGEMENT Filed Oct. 4, 1965 4 Sheets-Shet 4 I: I!" V (I) Q g 3 m 0 I 8 #T vQ /fl/ :2 I v G I 9' N u. Q J 4 v Y, 0 I

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United States Patent Office 3,372,823 Patented Mar. 12, 1968 ABSTRACT OF THE DISCLOSURE A tilting mechanism for a translatable lift truck mast in which the mast is supported at its base both by rollers seated upon horizontally-extending trackways and by plate means, and in which a non-rotatable assembly which is horizontally translatable with the mast carries rotatable carn means, so that rotation of the cam means tilts the mast about the axis of the mentioned rollers.

This invention relates to material handling apparatus, and more particularly, to an improved arrangement for controllably tilting the mast on lift trucks and the like. Usual lift trucks carry lifting masts up and down which load carriages are raised and lowered, usually hydraulically, with the load carriages carrying forks or other load-engaging devices. To allow a load to be placed on a shelf or taken from a shelf while the truck chassis remains stationary, it is common either to project the load carriage several feet to and from a mast which is fixed relative to the truck chassis by means of a scissors reach mechanism, or alternatively, to move the mast itself along the truck chassis. The present invention pertains to lift trucks of the latter, or sliding mast type.

The forks used on a typical load carriage extend forward in cantilever fashion, and hence the load applies a bending moment to the mast, tending to bend the mast forward and lower the tips of the forks. Such deflection if not compensated for, may cause a load being stored to scrape against other loads already stored on a shelf or in a rack, or may require that unnecessary vertical space be wasted as clearance space. It has become common to compensate for mast deflection due to a load by applying a controlled reverse deflection or tilt to the mast. Mast tilting also serves to cradle a load in the forks to prevent a load from falling off the forks. When a heavy load causes the mast to deflect, the amount of deflection of the mast and the resultant amount of displacement of the forks both depend, of course, upon the magnitude of the load. Because load sizes frequently vary, and because a truck may approach a shelf with the forks either loaded or unloaded, it is impractical to provide a fixed and unvarying amount of reverse tilt to compensate for mast deflection, and hence most (if not all) tilting mechanisms allow the operator to apply a desired amount of reverse mast tilt to compensate for mast deflection due to load.

Since the truck mast carries tremendous vertical loads, the pivotal connection between mast and truck chassis must necessarily be sizeable. It is a fairly simple matter to provide a suitable tilt mechanism for a mast which only pivots with respect to a truck chassis, but considerably more difiicult to provide a mast tilt mechanism for a mast which slides or translates along or across the truck chassis as Well as pivoting with respect to the truck chassis. In one prior art system the mast is slidably mounted in a pair of substantially horizontal track members which are themselves pivotably connected at one end to the truck chassis to be capable of being tilted slightly away from horizontal. The hydraulic cylinder provided to tilt the track members is connected between the tracks and the truck chassis. This prior system is disadvantageous in that tilting of the tracks away from horizontal in order to tilt the mast results in the mast having to be driven uphill or downhill in order to propel it forward or backward, so that the electric motor or other motive means used to translate the mast must work against components of the weight of the load and the Weight of the mast, load carriage, etc., requiring a much more powerful mast translation system than would otherwise be necessary, as well as being wasteful of power. In another prior art mast tilt system, the mast is pivotably connected to structure which does not tilt with respect to the chassis, and a hydraulic cylinder connected between the structure and the mast tilts the mast as the cylinder expands or contracts. In order to provide a sufiicient tilting moment with a hydraulic cylinder of reasonable size, a significant lever arm distance must exist between the mast pivot connection and the hydraulic cylinder connection, and the requirement for such a distance wastes valuable space on a narrowaisle lift truck. Various mast tilting arrangements which are suitable for trucks having non-translatable masts are obviously unsuitable if the mast must slide as well as pivot, many of them because they tend to interfere with the drive mechanism used to translate the mast as they pivot.

Thus, it is a primary object of the present invention to provide an improved mounting and tilting arrangement for a lift truck mast which must also be translated horizontally.

It isanother object of the invention to provide a mast arrangement of the type described which does not require the mast translating mechanism to drive the mast vertically in order to translate it horizontally.

Because the disposition of extremely heavy loads is controlled by mast tilting, it is very important that tilting be controlled as smoothly as possible. In some prior art rnast-tilting mechanisms the amount of mast tilt undesirably has been proportional to the radius of a crank arm operated by a hydraulic cylinder, so that an undesirably long crank arm must be employed. Smooth control is most easily obtained if a relatively large amount of hydraulic piston travel causes a relatively small amount of mast tilt. Large-angle motion of a crank arm also undesirably introduces a cosine function. The invention, as well as allowing a large hydraulic stroke to provide a small mast tilt angle, operates substantially linearly, so that a given hydraulic flow results in substantially constant mast tilting rate, and because of the mechanical advantage provided by certain cam means in the present invention, a much smaller hydraulic cylinder may be used to tilt the mast. Thus, it is another object of the invention to provide a lift-truck mast-tilting arrangement which requires only a small hydraulic cylinder to operate smoothly.

Other important objects of the invention are to provide a mast tilting arrangement which occupies a minimum amount of space, and which is therefore suitable for use on compact narrow-aisle lift trucks.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts, which will be exemplified in the construction hereinafter set forth, and the scope of the invention .Will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIG. 1 is an isometric view of a side-loader lift truck having a mast mounting structure equipped with the invention;

FIG. 2 is a plan view of one form of mast tilting mechanism constructed in accordance with the present 3 invention; with the mechanism shown positioned in relation to a load carriage, but with the truck chassis and various portions of the load carriage lifting mechanism removed;

FIG. 3 is an elevation view taken along lines 3 -3 in FIG. 2, with certain portions removed, but with several portions of the truck chassis shown added; and

FIG. 4 is an elevational cross-section view taken at 44 in FIG. 3.

Referring first to FIG. 1, the side-loader lift truck is provided with a base or chassis having front and rear platforms I2 and 14 carried by pairs of wheels 1619, with only the wheels 16 and 18 being Visible in FIG. 1. The truck includes fixed chassis structure interconnecting platforms I2 and I4 at one side of the truck, and an operators station 22 with various controls is shown situated atop platform 12. Situated between platforms 12 and 14, and movable sidewise on the track is mast structure 30. Mast structure 3% is mounted to be movable transversely of the truck, and is mounted on rollers which nest in channel-recess trackways 34 and 36, only the outer end of trackway 36 being visible in FIG. 1. Trackway 34 extends parallel to trackway as on the opposite side of mast assembly 36. Trackways 34 and 36 comprise heavy C-shape sections welded to the base or chassis of the truck at the inner edges of end platforms 12 and 14. The mast structure 3t) carries a load carriage 38 which may be hoisted up and down the mast structure, and load carriage 38 carries a load-engaging means shown in FIG. 1 as comprising a pair of forks 4t), 49. A removable attachment 47 to load carriage 38 carries two more forks 58, 53. In usual side-loader material-handling applications elongated loads, such as encoiled rugs, for example, are picked up by positioning the truck aside the rug roll, and then advancing the mast forward, i.e., to extend forks 40, 4t) and 58, 58 in under the load. Then load carriage 38 (and the forks and the load) may be hoisted up the mast. In some applications the mast will comprise a telescopic structure of well-known type to allow the load to be lifted to a considerable height. In FIG. 1 the mast assembly includes a pair of inwardlyfacing channels 25, 26 in which a pair of telescoping I-beams 27 and 28 are nested. In many applications the elongated loads will be lifted only a short distance, to where they will clear the tops of platforms 12 and 14, the mast will then be retracted to position the load over the platforms, and then the load will be lowered to rest on the two platforms as the truck is driven to transport the load to another location. A reverse procedure is used to pick up the load from the platforms, carry it out beyond the platforms by traversing the mast, and then lower it by lowering the load carriage. As thus far described in detail the side-loader lift truck of FIG. 1 is entirely conventional. In order to cradle the load with the loadengaging forks or the like, and in order to compensate for mast deflection due to heavy loads, it is desirable to be able to controllably tilt the mast, as previously mentioned, and the invention centers around the manner in which the mast assembly 30 is made both tiltable and translatable. While illustrated in connection with a sideloader truck, it should be clearly understood that the present invention is applicable as well to ordinary frontend loaders having translatable masts, or other vehicles having translatable masts.

In FIG. 1 a toothed rack 37 is shown fixedly attached to the truck chassis just below trackway 36 in platform 12 and a similar toothed rack 35 (not shown in FIG. 1) is mounted below trackway 34 in platform 14. Trackways 34, 36 and toothed racks 35 and 37 all extend parallel to each other, sidewise of the track. As will be explained in detail below, the mast structure 30 is extended and retracted by means of motor-driven pinions on the movable mast structure which engage the two racks 35 and 37 on opposite sides of the mast structure. An apparent problem which must be overcome to provide a successful translatable tilting mechanism is that of maintaining the pinions properly meshed with racks 35 and 37 as the mast is tilted.

Some portions of the movable mast structure are better shown in FIGS. 2-4. In the plan view of FIG. 2 the mast includes a pair of primary uprights shown as comprising the pair of inwardly-facing channel members 25 and 26, in which the pair of I-shapes 27 and 28 are nested. Rollers such as 31 and 32 carried on stub shafts Z9, 29 fixed to upright channels 25 and 26 guide I-shapes 2'7 and 28 up and down channels 25 and 26 in order to telescope the mast. Rollers 39, 39 carried on stub shafts 33, 33 affixed to load carriage 33 allow load carriage 38 to be raised and lowered by conventional hydraulic cylinder means 43. Hydraulic hoses 49 and chains 51 (not shown in FIG. 2) are guided by sheaves 50, 59 in FIG. 2.

The lower ends of mast channels 25 and 26 are carried on crosspiece 11 which is rigidly attached on one side to side plate 43 and on the other side to side plate 44. Side plates 43 and 44 carry stub shafts 45 and 46 upon which large rollers 56 and 57 are mounted. As best seen in FIG. 2, rollers 56 and 57 are mounted on axis x-x on opposite sides of the mast assembly, with axis xx slightly forward from the front faces of mast channels 25 and 26, thereby locating rollers 56 and 57 beneath the point of maximum vertical "load. Rollers 56 and 57 support most of the weight of the mast, the load carriage and the load, and these rollers roll along the top faces 60 and 61 of the top flanges of trackways 34 and 36, as best seen in FIGS. 3 and 4, as the mast is translated in or out.

As best seen in FIG. 4, a hydraulic tilt cylinder 65 is pivotally connected to plate 67 which is tied to and supports the mast, and the piston end 66 of hydraulic cylinder 65 is pivotally connected to crank arms 71 and 71', the arms being fixedly attached to cam shaft 74, so that expansion and retraction of the hydraulic cylinder-piston assembly 65-66 operates to rotate cam shaft 74. As best seen in FIG. 3, one end of cam shaft 74 passes outwardly through bushings E1 in plate 84 to carry an eccentric cam 85 which is keyed to shaft 74 by a conventional Woodruff key, and a roller which is nested within trackway 36. The other end of cam shaft 74, which shaft is shown partially cutaway in FIG. 3, similarly passes outwardly through a bushing (not shown) journalled in plate 33, and carries a similar eccentric cam 86 (not shown) and the other end of shaft 7 is similarly supported by roller 89 which nests within trackway 34. As best seen in FIG. 4, eccentric cam 85 bears against a circular hole 87 in side plate 44, and as cam 85 is rotated, the right-hand end of side plate 44 is raised or lowered. It is important to note, however, that plates 83 and 34 are neither tilted nor raised or lowered as the mast is tilted. The vertical disposition of plate 84 is determined at one point by shaft '74 as explained above, and a further roller 53 carried on stub shaft 55 mounted in and bolted to plate 84 fixedly secures plate 84. An enlarged clearance hole 59 is provided in side plate 44-, so that plate 44 may be cammed to tilt while plate 84- remains at a fixed angle and fixed height. Another roller 52 on the opposite side of the mast assembly similarly fixes plate 83, while allowing side plate 43 to tilt as cam shaft 74 rotates.

Being carried on rollers 89, 9t, in trackways 34, 36 which are mounted a fixed vertical distance above the floor, it will be seen that cam shaft 74 will not move vertically as the hydraulic cylindenpiston assembly is operated to rotate shaft 74.. However, as shaft '74 rotates, eccentric earns 85 and 35 carried on and keyed to shaft 74 will operate tilt side plates 43 and 44, causing them, and all the mast structure tied to them, to pivot about the center of rollers 55 and 57. By provision of a very gradual rise on cams 85 and 86, the mast assembly may be made to tilt as little as desired for a given hydraulic cylinder stroke distance, and the relationship between cylinder stroke and mast tilt may be made as linear as desired.

As seen in FIG. 3, mast traverse drive motor M is con nected through gearing 93 to rotate traverse drive shaft 91, which is journalled in bearings 94, 94 and carries drive pinions 41 and 42, which mesh with racks 35 and 37 carried on the bottoms of trackways 34 and36. Motor M is carried on bracket 62 which is rigidly attached to plate 83, Because plates 83 and 84 carrying drive shaft 91.need neither tilt nor move vertically with respect to thdf truck chassis as the mast assembly is tilted, drive pinions 41 and 42 always mesh properly with racks 35 and 37.

Stops, such as stop 68 on trackway 36 are mounted on each trackway to limit outward travel of the mast assembly, as shown in FIG. 4. Roller 69 in FIG. 4 is carried on a stub shaft in side plate 44, and has a diameter somewhat less than the inside height of the channel recess in trackway 36. Roller 69 acts as a safety roller, and does not normally engage either flange of the trackway channel. If the mast assembly were to tilt too far, however, roller 69 would engage one flange and prevent further mast tilt, which otherwise might lead to overturning.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are etficiently attained, and since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. Material handling apparatus, comprising, in combination: a vehicle chassis having a pair of mutually parallel horizontally-extending trackways; a mast assembly trnaslatable along said trackways relative to said chassis and tiltable at any position of translation; first roller means for mounting said mast assembly to roll along said trackways; a cam shaft; second roller means for mounting said cam shaft to roll along said trackways; a crank arm rigidly attached to said cam shaft; cam means attached to said cam shaft; an expansible and retractable hydraulic cylinder-piston assembly connected between said mast assembly and said crank arm and operable to rotate said cam shaft, said cam means being arranged to tilt said mast assembly with respect to said chassis upon rotation of said cam shaft; rack means carried on said chassis; plate means journalled on said cam shaft; third roller means for mounting said plate means to roll with respect to said trackways; drive shaft means journalled in said plate means; a pinion carried on said drive shaft and engaging said rack means; and motive means attached to said plate means and connected to rotate said drive shaft means.

2. Material handling apparatus, comprising in combination: a vehicle chassis; a mast assembly having a cam surface portion; first mounting means for supporting said mast assembly to allow said mast assembly to rotate about a first axis and to translate relative to said chassis along a first generally horizontal line; a rotatable cam shaft carrying cam means; second mounting means for mounting said cam shaft to translate relative to said chassis along a second line parallel to said first line; and motive means for rotating said cam shaft, said'cam means being adapted to act against said cam surface portion of said mast assembly to rotate said mast assembly about said first axis as said cam shaft is rotated.

3. Apparatus according to claim 2 in which said first mounting means comprises bearing surface means extending horizontally along said chassis and roller means connected to said mast assembly and engaging said hearing surface means to allow said mast assembly to rotate about said first axis.

4. Apparatus according to claim 2 in which said sec ond mounting means comprises bearing surface means extending horizontally along said chassis; a translatable non-rotatable second assembly; and roller means connected to said member and engaging said bearing surface means to allow said member to translate along said second line, said rotatable cam shaft being rotatably journalled in said second assembly.

5. Apparatus according to claim 2 in which said motive means comprises an expansible and retractable hydraulic piston-cylinder assembly.

6. Apparatus according to claim 4 having further motive means carried on said second assembly and drive means interconnecting said further motive means and said chassis to translate said mast assembly and said second assembly in a horizontal direction.

7. Apparatus according to claim 6 in which said further motive means comprises a motor having a rotatable output shaft.

8. Apparatus according to claim 6 in which said drive means includes a pinion connected to be driven by said further motive means and a toothed rack means extending horizontally along said chassis, afiixed to said chassis and disposed to mesh with said pinion.

References Cited UNITED STATES PATENTS 3,151,755 10/1964 Quayle 214-670 HUGO O. SCHULZ, Primary Examiner, 

